CSLB General Building (B)Framing and CarpentryMedium
A framer is installing a built-up wood header over a 9-foot-wide garage door opening in an exterior bearing wall. Compared to a 4-foot window opening in the same wall, why does the wider opening require more jack studs (trimmers) at each end?
- AThe header's bending capacity is unaffected by span, so jack studs are only for looks
- BA longer header span increases the end reaction load, requiring more bearing area from additional jack studs
- CWider openings always require a steel header instead of wood
- DBuilding codes require exactly one jack stud per foot of header length regardless of load
Show answer & explanationAnswer & explanation
Correct answer: B. A longer header span increases the end reaction load, requiring more bearing area from additional jack studs
As header span increases, the tributary roof/floor load carried by the header increases, which increases the reaction force delivered to each end. Additional jack studs provide the bearing area and load path needed to safely transfer this larger reaction into the foundation.
Why the other options are wrong
- A. Header bending capacity and required bearing very much depend on span and load.
- C. Steel is not automatically required; wood built-up or engineered headers can span this width.
- D. There is no such flat per-foot jack stud rule in the code; sizing is load-based.
Header Reaction & Jack Studs
The end reaction of a header increases with span and load, requiring adequate jack stud bearing area to transfer that load down to the foundation.
- Reaction load = half the total header load for a simple span
- Jack studs (trimmers) carry header reactions to the sill/foundation
- Wider spans and heavier loads require more jack studs or larger studs
Memory trick: 'Bigger span, bigger load, more studs to carry the road.'